1. Field of the Invention
The present invention relates to a communication system (communication method) using the asynchronous transfer mode (ATM), more particularly relates to a technique for ATM real-time communication which reduces the load on a communication bus and maintains the quality of services requiring which real-time processing.
2. Description of the Related Art
Computer technology and communications technology have been converging leading to the practical use of ATM in communications systems for transmitting a variety of information. Experiments are underway on application of ATM to audio data, video data, computer information, and other multi-media communications.
An ATM communications terminal (communications device) is often constructed using a network interface card (NIC).
FIG. 1 is a block diagram of the configuration of an ATM communications device (NIC) as an example of a general ATM communications device. An ATM communications device is most frequently used connected to a local PCI bus and, for example, has the configuration shown in FIG. 1. Note that this PCI bus is a 32-bit local bus developed by Intel Corporation.
An ATM device 2 shown in FIG. 1 is provided between an optical fiber 1 and a PCI bus 8.
The ATM device 2 comprises, as a transmitting system, a PCI bus interface 7, a segmentation device 5, a physical layer device 4, and an optical link 3 and, as a receiving system, the optical link 3, the physical layer device 4, a reassembly device 6, and the PCI bus interface 7. The optical link 3, the physical layer device 4, and the PCI bus interface 7 are used in both the transmitting system and the receiving system.
The operation of the receiving system in the ATM communications device 2 will be explained next. An ATM cell of an optical signal is transmitted through the optical fiber 1 and received by the optical link 3. In the optical link 3, the received optical signal is converted to an electric signal which is then converted to a cell form in the physical layer device 4. The converted cells are further converted to a packet form so that an upper layer can be used in the reassembly device 6. The packets are output via the PCI bus interface 7 to the PCI bus 8.
The received and converted packets output to the PCI bus 8 are transferred, for example, to a memory 19 or to other devices 13, 15, 18, 19, and 20 as shown in FIG. 2.
FIG. 2 is a block diagram of an ordinary ATM terminal device.
The ATM device 2 is connected via the PCI bus 8 to CPU bus 17. The CPU bus 17 is connected to the above mentioned ATM communications device 2 and to an ATM terminal comprised of an MPEG (Moving Picture Experts Group) decoder 13, an MPEG encoder 15, a CPU 18, a memory 19, and a display 20. The MPEG decoder 13 is connected to a television monitor 14. The MPEG encoder 15 is connected to a video camera 16.
Next, an explanation will be made of the operation of the transmitting system in the ATM communications device 2. When a packet is transmitted from the memory 19 or from other devices connected to the CPU bus 17 as shown in FIG. 2 to the PCI bus 8, it travels through the PCI bus interface 7 in the ATM device 2 and is divided into 53-byte cells at the segmentation device 5. The plurality of cells are then transmitted via the physical layer device 4 to the optical link 3, then to the optical fiber 1.
The strong feature of ATM communications is its ensuring of a real-time property, that is, it being designed to assure the necessary frequency bandwidth. In many cases, however, a real-time property cannot be ensured in the strict sense of the term with a PCI bus 8, given as an example of a local bus, or at an ordinary CPU bus, in ATM used for video signals, computer information, or other multi-media communications.
Generally, information transmitted in real time is small in packet size, for example, 188 bytes in a transport stream of the MPEG2. Therefore, in multimedia communications, for example, when transmitting a large amount of information, which is typical in compressed motion picture information, there are frequent requests for bus occupation rights. Furthermore, when the same bus is used for heavy load, that is, frequent access, large transmission volume devices, for example, in FIG. 2, the memory 19 or other devices 13, 15, 18, and 20, the occupancy ratio of these devices on the bus becomes high and a real-time property cannot be assured in frequent cases.
An object of the present invention is to provide an ATM terminal (device) connected to an ATM network which can reduce the load on a communication bus in real-time communication by ATM without causing a deterioration in the quality of services requiring a real-time property.
According to a first aspect of the present invention, there is provided an ATM communications device comprising a physical layer processing means, connected to an ATM communication network, for performing processing for converting between first data in the ATM communication network and second data in the ATM communications device; a separating means for separating the converted data into real-time data to be communicated in real time and non real-time data not to be communicated in real time; a real-time data processing means for performing processing for communication of the real-time data and outputting the processed real-time data; and a non real-time data processing means for performing the processing for communication of the non real-time data and outputting the processed non real-time data.
Preferably, the real-time data comprises a first identifier, the non real-time data comprises a second identifier, and the separating means separates the real-time data and the non real-time data by identifying the first identifier and/or the second identifier.
Preferably, the first and second identifiers are permanent virtual channel type identifiers.
Preferably, the first and/or second identifiers are virtual path type identifiers and/or virtual channel type identifiers.
According to a second aspect of the present invention, there is provided an ATM communications device comprising a real-time inputting means for receiving real-time data for real-time communication; a non real-time inputting means for receiving non real-time data for non real-time communication; a real-time data processing means for performing processing for communication of the real-time data and outputting the processed real-time data; a non real-time data processing means for performing processing for communication of the non real-time data and outputting the processed non real-time data; and a selecting means for receiving the processed real-time data and the processed non real-time data and preferentially selecting the real-time data.
According to a third aspect of the present invention, there is provided an ATM communications device comprising a real-time bus means for input and output of real-time data for real time communication; a non real-time bus means for input and output of non real-time data for non real-time communications; a real-time data processing means for performing processing for communication of the real-time data and outputting the processed real-time data; a non real-time data processing means for performing processing for communication of the non real-time data and outputting the processed non real-time data; a selecting means for receiving the processed real-time data and the processed non real-time data and preferentially selecting the input real-time data; a physical layer processing means, connected to an ATM communication network, for performing processing for converting between first data in the ATM communication network and second data in the ATM communications device; a separating means for separating the converted data into real-time data to be communicated in real time and non real-time data not to be communicated in real time; a real-time data processing means for performing processing for communication of the real-time data and outputting the processed real-time data; and a non real-time data processing means for performing processing for communication of the non real-time data and outputting the processed real-time data.
Preferably, the real-time bus means comprises a first real-time bus and a second real-time bus, the first real-time bus receives the real-time data, and the second real-time bus outputs the real-time data.
According to a fourth aspect of the present invention, there is provided a method of ATM communication including the steps of performing processing for converting between first data in an ATM communication network and second data in an ATM communications device; separating the converted data into real-time data to be communicated in real time and non real-time data not to be communicated in real time; performing processing for communication of the real-time data and outputting the processed real-time data; and performing processing for communication of the non real-time data and outputting the processed real-time data.
According to a fifth aspect of the present invention, there is provided a method of ATM communication including the steps of receiving real-time data for real time communication; receiving non real-time data for non real-time communication; performing processing for communication of the real-time data and outputting the processed real-time data; performing processing for communication of the non real-time data and outputting the processed non real-time data; and receiving the processed real-time data and the processed non real-time data and preferentially selecting the real-time data.
Further, according to a sixth aspect of the present invention, there is provided a method of ATM communication including the steps of receiving real-time data for real-time communication; receiving non real-time data for non real-time communication; performing processing for communication of the real-time data and outputting the processed real-time data; performing processing for communication of the non real-time data and outputting the processed non real-time data; receiving the processed real-time data and the processed non real-time data and preferentially selecting the real-time data; performing processing for converting between first data in the ATM communication network and second data in the ATM communications device; separating the converted data into real-time data to be communicated in real time and a non real-time data not to be communicated in real time; performing processing for communication of the real-time data and outputting the processed real-time data; and performing processing for communication of the non real-time data and outputting the processed non real-time data.